Synthesis of wittichenite Cu₃ BiS₃ thin films by sulfurizing thermally evaporated Cu-Bi metallic stacks

Wittichenite Cu₃BiS₃ thin films have received significant interest as light harvesters owing to their suitable optoelectronic properties and presence of earth-abundant, and non-toxic elements. We have synthesized Cu₃BiS₃ thin films by a two-stage process; in which, Cu/Bi/Cu metallic stacks were thermally evaporated and then sulfurized at 400^oC for 10–60 min in a quartz tubular furnace. The influence of sulfurization time on the structural, microstructural, compositional, optical, and electrical properties of the films was investigated. The results revealed that the films were orthorhombic Cu₃BiS₃ with the following lattice parameters: a = 0.768 nm; b = 1.043 nm; and c = 0.674 nm. Films uniformity, compactness, and crystal grain size increased upon increasing the sulfurization duration. On increasing the sulfurization time, the elemental stoichiometry of the films improved, and the direct optical bandgap increased from 1.38 to 1.40 eV. Additionally, Cu₃BiS₃ films exhibited p-type electrical conductivity and the electrical resistivity decreased with the increasing sulfurization time. Consequently, the Cu₃BiS₃ films synthesized at 30-and 60-min sulfurization durations can be applied to thin-film solar cells.